With JASSO you have to already be enrolled at the Japanese institution. These institutions all require the full tuition be paid upfront, and then there's no guarantee I'd even get the scholarship. I've tried rotary as well, but that requires at least a years notice, and there are very few scholarships compared to how many people apply. All other scholarships I've found stipulate that you have to go through a university outside of Japan. Including MEXT. Very counter-intuitive.
I agree with you entirely about being better able to learn in Japan. Unfortunately, I have tried talking to every single job I've found that will sponsor visas. I even spent hundreds of dollars to go to Chicago for an AEON interview. (Which I have to advise people never to do. Huge waste of time and money for every person in my group except one. Plus, the interviewers were jerks.) Every last job has either turned me down or not responded. I've got loads of offers to go to Korea, though... Apparently, the fall of NOVA has left an overflow of jobless English teachers in Japan.
And JET applications are another year away. There's no guarantee there either.
So, this is the last thing that I can think of. Go through an MA program, get a fellowship and/or student loans, and do a study abroad through them. I might even receive the MEXT or other scholarships like it for research.
If I've got something wrong, or anyone has another suggestion, I would love to hear it. After months of brick walls, I'm starting to get depressed about the whole thing.